Molded case circuit breakers for industrial application are described within U.S. Pat. No. 3,155,803 entitled "Electric Circuit Breaker With Toggle Positioning Means" in the name of Keith W. Klein and David B. Powell. This patent describes a toggle operating mechanism which consists of a pair of upper and lower links joined together by a toggle pin. To set the alignment of the upper links when the circuit breaker contacts are closed, the cradle is provided with a stopping surface at the forward end of the cradle to receive the toggle pin when the operating handle is moved to the ON position. The angle defined between the upper and lower links is maintained slightly less than 180.degree. to allow manual opening of the contacts without undue resisting force.
The advent of rapid operating mechanisms within industrial size molded case circuit breakers allows the circuit to be interrupted in a time during the current waveform before the current amplitude has reached a maximum value. The following U.S. patent applications describe various operating mechanisms and contact arm configurations which accomplish the rapid contact separation without requiring a re-design of the other breaker components. U.S. patent application Ser. No. 479,616 filed Mar. 28, 1983 now U.S. Pat. No. 4,480,242 entitled "Variable Torque Contact Arm For Electric Circuit Breakers"; U.S. patent application Ser. No. 479,617 filed Mar. 28, 1983 now U.S. Pat. No. 4,482,877 entitled "Electric Circuit Breakers Having Fast Short Circuit Response"; and U.S. patent application Ser. No. 609,053 filed May 10, 1984 now U.S. Pat. No. 4,554,119 entitled "Electric Circuit Breaker Having Reduced Arc Energy" all in the names of R. Castonguay and C. Jencks. These patent applications are incorporated herein for purposes of reference.
To facilitate such rapid contact separation, an S-shaped contact arm configuation is generally required. It was discovered during excessive high current test conditions, that the separating contacts would arc at the approximate location at which the contacts would mate upon closing. This could cause localized contact heating upon repeated opening and closing of the contacts under excessive current test conditions eventually causing the silver contact material to melt and fuse the contacts.
It was further discovered that the same contact arm configuration allowed the contacts to separate to an approximate 90.degree. angle measured between the upper and lower links resulting in a large separation distance between the contacts when the contacts are manually opened to set the operating mechanism. When the contacts were summarily closed, the force required to overcome the large separation distance caused the movable contact to strike the fixed contact with a substantial velocity causing the movable contact to bounce away from the fixed contact. This "contact bounce" between energized breaker contacts could cause localized arcing between the contacts increasing contact wear as well as providing contact weld as described earlier.
The purpose of this invention is to provide means for setting the contact separation distance upon manual opening of the contacts to thereby substantially reduce the stress on the mechanism and the occurrence of contact bounce and contact welding upon manual closing of the contacts.